Voltage converter circuits are used to convert an input voltage to an output voltage. Such voltage converters may convert a DC (Direct Current) voltage to another DC voltage, a DC voltage to an AC (Alternating Current) voltage, an AC voltage to an AC voltage or an AC voltage to a DC voltage, depending on the type of voltage converter.
Some types of voltage converters are referred to as switched mode power supplies (SMPS) which use switches together with capacitors and/or inductors to perform the voltage conversion. The switches are operated in a certain duty cycle to reach a desired output voltage. Voltage converters of these types include buck converters, boost converters or buck-boost converters.
One particular type of converters related to buck-boost converters are flyback converters, which are used in both AC/DC and DC/DC conversion. Flyback converters provide a galvanic isolation between an input and an output thereof by splitting an inductor used in a conventional buck-boost converter to form a transformer, the transformer providing galvanic isolation. In such flyback converters, the input voltage is applied at a circuit part coupled to a primary side of the transformer, while an output voltage is generated in a circuit part coupled to a secondary side of the transformer.
To maintain the galvanic isolation, a control circuit controlling switching of one or more switches of the second circuit part needs to be supplied on the second circuit part side and cannot for example use the input voltage directly as a supply, as this would break the galvanic isolation.
Conventional approaches use for example an additional winding in the transformer to generate such a supply voltage. This additional winding, however, increases the costs of the circuit. Therefore, a need exists for voltage converter circuits providing a stable supply voltage which are comparatively cheap to implement.